1. Field of the Invention
The present invention relates to an electronic control apparatus for a vehicle for performing control an alternator in association with controlling the number of revolutions of the engine during idling.
2. Discussion of Background
There has been known a method of controlling generation of electricity in an alternator, as shown in, for instance, Japanese Unexamined Patent Publication No. 222099/1984, in which a load current is detected and an electrical voltage is changed depending on the value of detected load current.
Further, in a method of controlling the number of revolutions during idling in association with control of an alternator, there has been known, for instance, Japanese Unexamined Patent Publication No. 170553/1988 in which air quantity is controlled. In the publication, a current through an electrical load is detected and the number of revolutions of the engine during idling is controlled depending on the detected load current.
A technique of controlling an alternator is disclosed in, for instance, Japanese Unexamined Patent Publication No. 248238/1986. In this technique, an output current from an alternator is determined from an intermittent signal produced by feeding and interrupting a current to the field coil of the alternator, i.e. a field duty signal, and the current to be supplied to the field coil is forcibly turned off in an increase of the duty, and thereafter, the current is turned on to perform control for gradually increasing the duty.
The conventional control of generation of electricity in the alternator is conducted based on either a load current or a battery charging current, and accordingly, when the generation of electricity is stopped when a small load current is being provided, the charging to the battery is insufficient. On the other hand, when the generation of electricity is stopped when a large charging current is being provided to the battery, a danger of exhaustion of the battery exists. Further, when the generation of electricity is stopped when small charging current is being provided to the battery, there is a problem that the battery may be exhausted when a large electrical load is applied.
In controlling the number of revolutions of the engine during idling in association with controlling an alternator, there are two techniques: a technique of controlling an air quantity in response to an electrical load current and a load-responsive control technique wherein the output of the alternator is stopped by controlling the same when the output of the alternator is increased, and thereafter, the output is gradually increased.
In the former case, it is impossible to prevent a drop of revolution number at the initial stage of the connection of an electrical load since the air quantity is controlled. On the other hand, in the later case, it is also impossible to prevent a drop in the number of revolutions of the engine at the time of the connection of an electrical load since determination is made upon an increase in the field duty.
In a case that the output of the alternator is forecast from a field duty, an output current is obtained from the calculation of a field duty multiplied with a revolution number of engine when a load to the engine is light. However, in this technique, there is a large error because a resistance in the field coil is changed by an ambient temperature, whereby the performance of control is poor.